Seamless steel pipe is a kind of strip steel with hollow section and no seams around. Steel pipe has a hollow section, a large number of which are used as pipes transforming fluid, such as oil, natural gas, coal gas, water and some solid materials, and so on. Compared with solid steel such as round steel, steel pipe is lighter in condition that bending resistance and torsional strength are the same, is a kind of economic cross section steel and widely used in the manufacture of structural and mechanical parts, such as petroleum drill pipe, auto transmission shaft, bicycle frame and construction of steel scaffolding, etc. Using steel pipe to manufacture annular parts can improve material utilization, simplify the manufacturing process, save material and processing time, for example, rolling bearing ring and jack sets are widely made from steel pipe at present. Steel pipe is also indispensable material for all kinds of conventional weapons, for instance, gun and gun barrel are made from steel pipe. Steel pipe can be divided into circular tube and special pipe according to cross-sectional area of different shapes. Due to the fact that when the circumference is equal, circle area is the largest, so circular tube can deliver more fluid. What’s more, when circle cross section is under radial pressure from internal or external, the stress is relatively uniform, therefore, the vast majority of steel pipes are round. However, circular pipes have some limitations, for instance, in condition of plain bending, bending strength of circular pipes is not as good as square and rectangular pipes, rectangular pipe is commonly used for agricultural machinery and skeleton and steel wood furniture.

Welded steel pipe is also called welded pipe, made from steel plate or steel strip after being crimped molding. Product technology of welded steel pipe is simple, with high production efficiency, various specifications and low equipment investment, but in general the strength is lower than that of the seamless steel pipe. The strength of spiral welded pipe is generally higher than that of straight seam welded pipe, less billet can be applied to produce larger diameter welded pipe and you can also use the same width of billet to produce welded pipe of different diameter. But compared with the same length of straight seam pipe, weld length increases by 30 to 100 percent, and the speed of production is low. As a result, small diameter welded pipes mostly apply straight seam welding, large diameter welded pipes mostly adopt spiral welding.